1. Field of the Invention
This invention relates to a three-dimensional image display device which displays a dynamic solid image using a hologram.
2. Description of the Related Art
Mechanical CADs generally use a three-sided figure and two-dimensional projection for displaying a shape of a three-dimensional object. It is, however, rather difficult to accurately recognize a complicated shape from a two-dimensional projected image. In order to observe an object in various directions in three-dimensional computer graphics, the image must be rotated on a display screen and hence it is difficult to grasp a whole image spatially.
A three-dimensional solid image is more preferable than a two-dimensional one to visualize the result of simulation of fluid or to display the shapes of bones and blood vessels on the basis of an ultrasonic diagnosis image or a CT (Computed Tomography) image. The formation of a dynamic solid image is desired to obtain an ambience even in the field of solid images.
Conventionally, a binocular solid display process is used usually to display a three-dimensional solid image. The binocular solid display process is to provide different images for the right and left eyes to obtain an image having a depth. When observing two objects different in depth with both eyes, the positions of the two object images formed on the retinas of right and left eyes deviate in proportion to the difference in distance between the objects. This quantity of deviation between the object images is called a binocular vision difference. When two dynamic or still images which contain information on the binocular vision difference are displayed, only image components for the right and left eyes are separately observed using a pair of special purpose glasses which uses a difference in color or polarization or a special display screen including an array of miniature optical elements, and a solid space is reproduced before and after the screen.
The binocular solid display process, however, reproduces a solid space with the binocular parallax alone on the basis of observation in one direction.
Thus, there are the following problems:
1) Information obtained in other directions is so insufficient that a change in the image depending on the position of the observation does not occur;
2) The device cannot be focused on an object which the observer wants to view;
3) Since the position of the image reproduction differs from that on the screen, focus adjustment is a process which is not encountered in daily life; and
4) Since the images which we view with our right and left eyes are different, we feel a sensation of incompatibility.
A holography display process has recently been marked as means for solving such problems. The holography is a technique for storing and reproducing both the amplitude and phase of an optical wave in a plane, so that even when a view point is moved vertically and horizontally, a three-dimensional image from different angles can be seen. Because all of physiological factors required for recognizing a solid object, the binocular vision difference, the congestion and the eye adjustment hold, the hologram can be more natural three-dimensional image than that obtained by the other methods. The hologram is produced by storing interference fringes occurring as a result of interference of optical waves called object light from an object and different optical waves called reference light coming from a different direction. When the reference light is entered into the hologram, the light is diffracted by interference fringes in the hologram so that the wave front same with the original object light is formed and thus an object image appears in the space.
However, the conventional holography display requires one hologram for each subject (image). Thus, while a solid (still) image has a very high solid property, a large amount of hologram is required and the device structure is very complicated when a dynamic image hologram is displayed.